1. Field of the Invention
The present invention relates to a yellow ZnS-based phosphor, a process of preparing the same and a display device using the phosphor. More particularly, the present invention relates to a yellow phosphor achieved by a ZnS-based host material having improved color coordinates and luminance for use in intermediate- and low-voltage display devices, and a process of preparing the same.
2. Description of the Related Art
Representative intermediate- and low-voltage display devices include vacuum fluorescent displays (VFDs) and field emission displays (FEDs). Like cathode ray tubes (CRTs), VFDs are self-radiating displays using phosphors, and are widely used, for example, as digital displays of household electric appliances and gauge panels of automobiles. Until recently, VFDs have mainly been used in low-capacity, small-sized products to simply display numbers, characters, and signs. However, VFDs are in use as high-density graphic image displays. In the near future, a full color VFD having a large display capacity will be commercially viable.
FEDs have received considerable attention as a next generation display device having the advantages of flat panel displays, such as liquid crystal displays (LCDs), and CRTs. Thus, a great deal of research on FEDs continues to be actively conducted. FEDs, which operate on the principle of field emission of electrons from microscopic tips, are known to be capable of overcoming the drawbacks of CRTs, such as excessive bulk and weight, and the drawbacks of LCDs, such as high manufacturing cost, limited size and viewing angle. Furthermore, since FEDs have various advantages such as a thin film form, low power consumption, low manufacturing cost, excellent temperature characteristics, and high-speed operation, FEDs have a wide variety of applications ranging from home televisions to industrial equipment and computers. In particular, FEDs are likely to be widely used in commercial applications such as notebook PCs, monitors, and televisions, like thin film transistor (TFT) LCDs.
A phosphor which is excitable by a low-velocity electron beam is required in VFDs or FEDs in order to emit light at a low anode drive voltage of less than 1 kV. Since such phosphors which are excitable by a low-velocity electron beam typically include sulfur in their host materials, these phosphors are generally referred to as sulfide-based phosphors. An example of sulfide-based phosphors are ZnS-based phosphors.
ZnS-based phosphors currently being used include a ZnS:Ag, Cl phosphor, a ZnS: Ag, Al phosphor, a ZnS:Cu, Al phosphor, a ZnS: Cu, Au, Al phosphor, and a ZnS: Mn phosphor. In particular, the ZnS: Mn phosphor is suitably used for intermediate- and low-voltage display devices. However, unlike the other ZnS-based phosphors using silver or copper as an activator, which are mostly blue-emitting phosphors, the ZnS: Mn phosphor using manganese emits yellow light. The ZnS: Mn phosphor emitting such characteristic color light leads to a wide range of applications. For light emitted by the ZnS: Mn phosphor, the x-coordinate is 0.55 and the y-coordinate is 0.43. Thus, the emission color is substantially orange, and therefore the ZnS: Mn phosphor is still open for improvement in luminance.